High gloss rubber modified monovinylidene aromatic polymers produced by a mass polymerization process

ABSTRACT

The present invention relates to a mass polymerized rubber-modified polymeric composition comprising a continuous matrix phase of a polymer of a monovinylidene aromatic monomer, and optionally, an ethylenically unsaturated nitrile monomer, and rubber particles produced from a functionalized diene rubber.

CROSS REFERENCE STATEMENT

This application claims the benefit of U.S. Provisional Application No.60/445,557, filed Feb. 5, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to rubber modified polymers obtained fromvinyl aromatic monomers.

Rubber modified polymers, such as high impact polystyrene (HIPS) andacrylonitrile-butadiene-styrene (ABS), are typically produced by masspolymerizing styrene or styrene/acrylonitrile in the presence ofdissolved rubber. ABS is more typically produced using an emulsionpolymerization process which produces small rubber particles and highgloss products, but with increased conversion costs.

In the preparation of rubber modified polymers, the rubber particle sizeand morphology play an important role in controlling the physicalproperties of the final product. The final rubber particle size can bedetermined by a number of different parameters including shear,viscosity, and interfacial tension. Increased shear after phaseinversion can be used to reduce particle size, however this adds expenseand complexity to the process. The final rubber particle size can alsobe influenced by the viscosity ratio of the disperse phase/continuousphase, and the viscosity of the continuous phase polymer. Sizing readilyoccurs when the viscosity ratio is between 0.2 and 1; and with higherviscosity of the continuous phase, the greater the ease of particlebreakup. The rubber phase viscosity is determined by the rubber leveland by the solution viscosity of the rubber. Additionally, grafting andcrosslinking of the rubber will increase rubber viscosity. Interfacialsurface tension will also influence rubber particle size and morphology,wherein a reduction of the interfacial tension can be achieved byutilizing the compatible block rubbers or by grafting to make compatiblerubbers in-situ. Compatible block rubbers are characterized by having ablock miscible with the continuous phase and a block miscible with thediscontinuous phase. A reduction of the interfacial tension willfacilitate the sizing process thereby increasing the flexibility. InHIPS compositions, compatible rubbers include styrene-butadiene blockrubbers. In ABS compositions, styrene-butadiene block rubbers are notcompatible since polystyrene is not miscible with the SAN continuousphase. SAN-butadiene block rubbers are compatible with ABS, but are notcommercially available. Therefore in ABS polymer compositions,compatible block copolymers have to be produced in situ via grafting.The use of functionalized rubbers has been investigated in order to makesuch compatible block rubbers in-situ in both HIPS and ABS processes dueto the economic advantage.

U.S. Pat. No. 5,721,320 by Priddy et al. discloses a free radicalpolymerization in the presence of a functionalized diene rubber having astable free radical group such that a vinylaromatic-diene block orcopolymer-diene rubber is formed. However, Priddy refers to theproduction of transparent HIPS and ABS, wherein the rubber particle sizeis very small (0.1 micron), which is insufficient for many high impactapplications.

U.S. Pat. No. 6,262,179 by Atochem discloses a process for producingvinyl aromatic polymers in the presence of a stable free radical.However, the resultant product has a very wide rubber particle sizedistribution, with a large average rubber particle size, which can isnegatively affect physical properties, such as gloss.

U.S. Pat. No. 6,255,402 by Atochem discloses a process of polymerizingat least one vinyl aromatic monomer in the presence of a rubbercomprising a group which generates a stable free radical. However, thisprocess utilizes a wide variety of rubbers, including those having highsolution viscosity, which can negatively affect physical properties, forexample, gloss, of the polymer.

U.S. Pat. No. 6,255,448 by Atochem discloses a process for thepolymerization of at least one monomer in the presence of a stable freeradical having substitution in the beta position. However, these betasubstituted stable free radicals can have increased cost and may not beused in anionic coupling due to the reactivity of the substituent.

WO 99/62975 by Atochem discloses a process using a stable free radicaland an initiator. This process also utilizes high viscosity rubberswhich can negatively affect gloss and other physical properties.

WO 01/74908 by BASF discloses a method of polymerization in the presenceof a stable free radical and a thiol compound. U.S. Pat. No. 4,581,429discloses the use of alkoxy amines (>N—O—X) in controlled radicalpolymerization, wherein the alkoxy amine forms a free radical (X.) whichis suitable as a free radical initiator and a stable free radical(>N—O.). However, this method does not include the production of rubbermodified polymers.

Therefore, there remains a need for an efficient and cost effective massprocess for achieving the rubber particle size, distribution andmorphology desired, utilizing in-situ produced block rubbers which offerenhanced physical properties and efficient processing.

SUMMARY OF THE INVENTION

The present invention relates to a mass polymerized rubber-modifiedpolymer composition comprising:

-   (i) a continuous matrix phase comprising a polymer of a    monovinylidene aromatic monomer, and optionally, an ethylenically    unsaturated nitrile monomer, and-   (ii) discrete rubber particles dispersed in said matrix, said rubber    particles produced from a rubber component comprising from 5 to 100    weight percent of a functionalized diene rubber having at least one    functional group per rubber molecule capable of enabling controlled    radical polymerization;    wherein the composition is further characterized by:    -   a) a volume average rubber particle size of from about 0.15 to        0.35 micron,    -   b) a total rubber phase volume between 12 and 45 percent, based        on the total volume of the combination of the matrix phase and        the rubber particles;    -   c) a partial rubber phase volume between 2 and 20 percent        characterized by rubber particles having a volume average        particle size of greater than 0.40 microns; and    -   d) a crosslinked rubber fraction of at least 85 percent by        weight, based on the total weight of the rubber particles.

This composition offers small average rubber particles size, and highrubber cross-linking, which are essential for high gloss and low glosssensitivity; while maintaining good toughness properties by the rubberphase volume and broad particle size distribution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Monovinylidene aromatic monomers useful for both the matrix and blockcopolymer, if used, include any vinyl aromatic monomers such as thosedescribed in U.S. Pat. Nos. 4,666,987, 4,572,819 and 4,585,825, and5,721,320 which are incorporated by reference herein. The optionalethylenically unsaturated nitrile monomer includes, but is not limitedto acrylic monomers such as acrylonitrile and methacrylonitrile.Additionally, the copolymer can comprise additional monomers such asother vinyl aromatics, methacrylic acid, methyl methacrylate, butylacrylate, acrylic acid, methyl acrylate maleimide, phenylmaleimide, ormaleic anhydride. Preferably the matrix polymer is polystyrene or acopolymer of styrene and acrylonitrile. The polymerization is conductedin the presence of predissolved elastomer/rubber to prepare impactmodified, grafted rubber containing products, examples of which aredescribed in U.S. Pat. Nos. 2,694,692; 3,123,655; 3,243,481; 3,346,520;3,639,522; 3,658,946 and 4,409,369; and which are incorporated byreference herein. The composition of the present invention particularlyrelates to compositions commonly referred to as high impact polystyrene(HIPS) and acrylonitrile-butadiene-styrene copolymers (ABS).

The Mw of the matrix phase can vary greatly dependent upon theapplications of the rubber modified polymer. Typically, the Mw can varyfrom 50,000 to about 300,000 amu. Mw is the weight average molecularweight measured using gel permeation chromatography with a polystyrenestandard.

Typically, the rubber component used in the composition of the presentinvention has a solution viscosity (5 percent in styrene at 20° C.) ofless than 200 centipoise (cps), generally, less than 100 (cps).Preferably, the rubber component used in the composition of the presentinvention comprises a low viscosity rubber having a solution viscosity(5 percent in styrene at 20° C.) in the range of 5 to less than 50centipoise (cps), preferably from 10, more preferably from 15, and mostpreferably from 20 to less than 45, preferably to less than 40, morepreferably to less than 35, and most preferably to less than 30 cps. Itis important to note that the rubber component may comprise more thanone rubber, and that any individual rubber may have a higher solutionviscosity, as long as the combined solution viscosity of all rubberswithin the rubber component is within the limitations taught above.

The rubber component must contain at least one functionalized dienerubber. Suitable functionalized diene rubbers include rubbers derivedfrom 1,3-conjugated dienes such as butadiene, isoprene, chloroprene orpiperylene, and the like. These rubbers include diene homopolymers, aswell as copolymers and block copolymers of alkadienes and a vinylaromatic monomer. Suitable functionalized copolymer rubbers forinclusion within the rubber component include copolymers of alkadienesincluding 1,3-conjugated dienes such as butadiene, isoprene, chloropreneor piperylene and a monovinylidene aromatic monomer. Preferably, thefunctionalized copolymer is a functionalized block copolymer wherein theblock produced from the monovinylidene aromatic monomer is at least 8weight percent, based on the total weight of the block copolymer. Theblock copolymers can contain any number of blocks such as AB, ABA, ABAB,ABABA, ABABAB and so on. Preferably, the functionalized block copolymerrubber contains at least 8, more preferably at least 10, and mostpreferably at least 12 to 40, preferably to 35, more preferably to 30and most preferably to 25 weight percent polymerized vinyl aromaticblock, based on the total weight of the block copolymer. It is knownthat a small amount of tapering can occur in the production of suchblock rubbers. The functionalized diene rubber may have anyarchitecture, such as linear or star branched, and a microstructurehaving any vinyl/cis/trans ratio, as long as the functionalized dienerubber meets the other requirements stated previously. Most preferredfunctionalized diene rubbers are functionalized diblock copolymers of1,3-butadiene and styrene.

Such rubbers are widely known in the art as well as methods for theirmanufacture as disclosed in Science and Technology of Rubber (AcademicPress,) Ed. James E. Mark, Burak Erman, Frederick R. Eirich-Chapter 2.VIII, pgs. 60–70.

The functionalized diene rubber contains a minimum of 1 functional groupper rubber molecule. The functional group is defined as a functionalitywhich enables is controlled radical polymerization. Controlled radicalpolymerization employs the principle of dynamic equilibration betweengrowing free radicals and dormant or unreactive species as disclosed in“Controlled/Living Radical Polymerization” (2000) p. 2–7 ACS Symposiumseries, 768.

The functionality included in the functionalized copolymer rubber canenable controlled radical polymerization through a number of differentmechanisms including by:

-   -   I) stable free radical polymerization, e.g. nitroxide mediated        polymerization;    -   II) metal catalyzed atom transfer radical polymerization (ATRP);    -   III) reversible addition-fragmentation chain transfer (RAFT);        and    -   IV) a degenerative transfer process based on a thermodynamically        neutral (at the propagation stage) exchange process between a        growing radical, and a dormant species; and        other degenerative transfer processes as described in “Chapter 1        Overview: Fundamentals of Controlled/Living Radical        Polymerization” of Controlled Radical Polymerization by        Matyjaszewski, 1998, pages 2–30 and Handbook of Radical        Polymerization, Ed. K. Matyjaszewski, T. P. Davis (Wiley) p.        383–384.

The functional group can be attached to the rubber utilizing anyacceptable method which places at least one functional group on thebackbone or chain end of the diene rubber. In one embodiment, thefunctional group is attached to the rubber via the end of the polymerchain and no random attachment of the functional group occurs on therubber polymer chain, for a maximum of 2 functional groups, one on eachend. Examples of such are included in U.S. Pat. No. 5,721,320. In apreferred embodiment, the functionalized diene rubber does not containany other functionalities which are reactive during the radicalpolymerization process, other than the typical unsaturation present indiene rubbers.

In one embodiment, the functional group will generate a stable freeradical which is capable of enabling controlled free radicalpolymerization. Stable free radicals include compounds which can act asradical polymerization inhibitors such as nitroxide radicals, forexample, 2,2,6,6,-tetramethyl-1-piperidinyloxy (TEMPO) as disclosed inU.S. Pat. No. 6,262,179 and U.S. Pat. No. 5,721,320, both of which areincorporated herein by reference. Other stable free radical compoundsinclude, but are not limited to2,2,6,6-tetramethyl-1-[1-[4-(oxiranylmethoxy)phenyl]ethoxy]-piperidineand3,3,8,8,10,10-hexamethyl-9-[1-[4-(oxiranylmethoxy)phenyl]ethoxy]-1,5-dioxa-9-azaspiro[5.5]undecane.

The stable free radical group is defined as a substituent which iscapable of forming a stable free radical upon activation as described inU.S. Pat. No. 5,721,320. Other nitroxy containing compounds can be foundin U.S. Pat. No. 4,581,429 by Solomon et al. which is incorporatedherein by reference.

Additionally, non-functionalized rubbers can be used in combination withthe functionalized diene rubbers within the rubber component. In thiscase, typically at least 5 weight percent of the rubber component is afunctionalized diene rubber, generally at least 10, preferably at least15, more preferably at least 20 and most preferably at least 25 weightpercent, based on the total weight of all rubbers within the rubbercomponent, to about 60, preferably to about 70, more preferably to about80, even more preferably to about 90, and most preferably to about 100weight percent. The non-functionalized rubber can be any rubbertypically used in rubber modified polymers including diene homopolymersand copolymers with vinyl aromatics; block copolymers, star branchedrubbers, linear rubbers, and the like.

The amount of rubber initially dissolved in the vinyl aromatic monomeris dependent on the desired concentration of the rubber in the finalrubber-reinforced polymer product, the degree of monomer conversionduring polymerization and the viscosity of the solution. The rubber istypically used in amounts such that the rubber-reinforced polymerproduct contains from about 2 to about 30 percent, preferably from about3 to about 20 percent, and more preferably from about 3 to about 15weight percent rubber, based on the total weight of the vinyl aromaticmonomer and rubber components, expressed as rubber or rubber equivalent.The term “rubber” or “rubber equivalent” as used herein is intended tomean, for a rubber homopolymer, such as polybutadiene, simply the amountof rubber, and for a block copolymer, the amount of the copolymer madeup from monomer which when homopolymerized forms a rubbery polymer, suchas for a butadiene-styrene block copolymer, the amount of the butadienecomponent of the block copolymer.

The rubber reinforced polymer can be prepared by dissolving thefunctionalized rubber in the vinyl aromatic monomer and polymerizing themixture in the presence of the functional group. This process can beconducted using conventional techniques known in the art for preparingrubber reinforced polymers such as high impact polystyrene (S) and ABS,which are described in U.S. Pat. Nos. 2,646,418, 4,311,819 and 4,409,369and are incorporated herein by reference.

Initiators may optionally be used in the process of the presentinvention. Useful initiators include free radical initiators such asperoxide and azo compounds which will accelerate the polymerization ofthe vinyl aromatic monomer. Suitable initiators include but are notlimited to tertiary butyl peroxyacetate, dibenzoyl peroxide, dilauroylperoxide, 1-3-bis-(tertiarybutylperoxy)-3,3,5-trimethyl cyclohexane,t-butylhydroperoxide, ditertiary-butylperoxide, cumene hydroperoxide,dicumylperoxide,1,1-bis(tertiary-butylperoxy)-3,3,5-trimethyl-cyclohexane,t-butylperoxybenzoate, 1,1-bis(t-butylperoxy)-cyclohexane,benzoylperoxide, succinoylperoxide and t-butyl-peroxypivilate, and azocompounds such as azobisisobutyro-nitrile,azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbo-nitrile,azobismethyl isolactate and azobiscyanovalerate.

Initiators may be employed in a range of concentrations dependent on avariety of factors including the specific initiators employed, thedesired levels of polymer grafting and the conditions at which the masspolymerization is conducted. Typically, the initiator is employed in arange from 50 to 500, preferably from 75 to 250, parts per million basedon the total weight of the initial feed.

Additionally, a solvent may be used in the process of the presentinvention. Acceptable solvents include normally liquid organic materialswhich form a solution with the rubber, vinyl aromatic monomer and thepolymer prepared therefrom. Representative solvents include aromatic andsubstituted aromatic hydrocarbons such as benzene, ethylbenzene,toluene, xylene or the like; substituted or unsubstituted, straight orbranched chain saturated aliphatics of 5 or more carbon atoms, such asheptane, hexane, octane or the like; alicyclic or substituted alicyclichydrocarbons having 5 or 6 carbon atoms, such as cyclohexane; and thelike. Preferred solvents include substituted aromatics, withethylbenzene and xylene being most preferred. In general, the solvent isemployed in amounts sufficient to improve the processability and heattransfer during polymerization. Such amounts will vary depending on therubber, monomer and solvent employed, the process equipment and thedesired degree of polymerization. If employed, the solvent is generallyemployed in an amount of up to about 35 weight percent, preferably fromabout 5 to about 25 weight percent, based on the total weight of theinitial feed.

Other materials/additives may also be present in the process of thepresent invention, including plasticizers, for example, mineral oil;flow promoters, lubricants, antioxidants, for example, alkylated phenolssuch as di-tertbutyl-p-cresol or phosphites such as trisnonyl is phenylphosphite; catalysts, for example acidic compounds such ascamphorsulfonic acid; mold release agents, for example, zinc stearate,or polymerization aids, for example, chain transfer agents such as analkyl mercaptan, for example, n-dodecyl mercaptan. If employed, thechain transfer agent is generally employed in an amount of from about0.001 to about 0.5 weight percent based on the total weight of thepolymerization mixture to which it is added. Additionally a lowmolecular weight additive having a surface tension of less than 30dyne/cm according to AST: D1331 at 25° C., such as polydimethylsiloxaneor a fluorinated polymer, can be added to the composition of the presentinvention. Typically, such additives are used in amounts of 0.05 to 0.5weight percent, based on the total weight of the composition.

The composition of the present invention is further characterized by:

-   -   a) a volume average rubber particle size of from about 0.15 to        0.35 micron,    -   b) a total rubber phase volume between 12 and 45 percent, based        on the total volume of the combination of the matrix phase and        the rubber particles;    -   c) a partial rubber phase volume between 2 and 20 percent        characterized by rubber particles having a volume average        particle size of greater than 0.40 microns; and    -   d) a crosslinked rubber fraction of at least 85 percent by        weight, based on the total weight of the rubber particles.

The rubber particle size can have either a broad monomodal particle sizedistribution defined by a polydispersity (D₂) as determined by(D_((z+1))/D_(n) as defined in the examples) of 1.25 or larger, or abimodal particle size distribution, with the total volume particle sizeaverage being from 0.15 to 0.35 micron, preferably from 0.15 to 3, morepreferably from 0.2 to 0.3 micron; with a rubber volume fraction between2 and 20 percent, characterized by rubber particles having volumeaverage particle size of greater than 0.40 micron. Therefore, at least 5percent of the rubber phase volume is made up of rubber particlesgreater than 0.40 microns. Typically, the remaining fraction of rubbercomponent will comprise volume average particle sizes which are smallerin order to meet the limitation of an overall volume average rubberparticle size of from 0.15 to 0.35.

The rubber-modified polymers of the present invention can have both abroad monomodal particle size distribution, or a multi-modal, forexample, bimodal particle size distribution. In either case, the rubbercomponents can comprise one rubber or a blend of rubbers. In particular,more than one rubber can be used in a monomodal or bimodal process. Abimodal rubber particle size distribution is defined as having twodistinct peaks of particles when grafted on axis' of particle size vs.volume fraction; one peak designating smaller particles and the otherpeak designating larger particles.

Typically, in a bimodal particle size distribution, the larger particlefraction will have a volume average particle size of from 0.5,preferably from 0.6, more preferably from 0.7 and most preferably from0.8 to 3, preferably to 2.5, more preferably to 2 and most preferably to1.5 microns. Typically, the smaller particle fraction will have a volumeaverage particle size of from 0.075, preferably from 0.1 to 0.3,preferably to 0.25, and more preferably to 0.2 microns. Particle sizesare determined using Transmission Electron Microscopy (TEM) analysis.

The composition of the present invention is further characterized by atotal rubber phase volume between 12 and 45 percent, based on the totalvolume of the combination of the matrix phase and the rubber particles;and a partial rubber phase volume of at least 2 percent, characterizedby rubber particles having a volume average particle size of greaterthan 0.40 micron. The partial rubber phase volume with a volume averageparticle size of greater than 0.4 micron is preferably between 2 percentand 20 percent, more preferably between 4 percent and 18 percent, andmost preferably between 6 and 16 percent.

Additionally, the composition of the present invention is furthercharacterized by a crosslinked rubber fraction of at least 85 percent byweight, based on the total weight of the rubber particles. Thecrosslinked rubber fraction is determined by measuring total rubber andsoluble rubber in the sample. The percent of cross-linked rubber iscalculated with the following equation:

${{Percent}\mspace{14mu}{crosslinked}\mspace{14mu}{rubber}} = \frac{\left( {{{total}\mspace{14mu}{rubber}\mspace{14mu}({Tr})} - {{soluble}\mspace{14mu}{rubber}\mspace{14mu}({Ts})}} \right) \times 100}{{total}\mspace{14mu}{rubber}\mspace{14mu}({Tr})}$

To measure the total rubber, 250 mg of sample is weighed to the nearest0.001 mg and placed in a vial to which 5 mL+0.1 mL of bromoform isadded. The sample is placed on a shaker for a minimum of 1.5 hours toinsure that the continuous phase is dissolved and that there are nosignificant pieces of undispersed rubber. The sample is then transferredto a 1 mm liquid FT IR cell and the sample is scanned from 4000 to 400cm-1. The rubber in the sample is determined by integrating the band at970 cm-1 (in the absorbance mode) and is calculating the amount ofrubber using external standard solutions of the rubber.

To measure the soluble rubber, the solution from above is placed in asuitable centrifuge tube and centrifuged for 10 minutes at 8000 G. Theclear bottom layer is then carefully removed using a syringe, placed inthe liquid cell and scanned by FT IR as described above. The amount ofsoluble rubber is calculated using external standard solutions of therubber. Note:

-   1) The bromoform used for this analysis must be spectroscopically    clean in the area of 1000–900 cm-1. This is accomplished by passing    the bromoform through a silica column. A blank of the bromoform    should be analyzed at least once per day to insure that the purity    has not changed.-   2) Care must be taken to insure that the liquid cell is thoroughly    cleaned in between analyses. Residue of rubber from previous samples    either in the cell or on the cell windows will seriously effect the    accuracy of the results.-   3) External standard solutions should be made to coincide with the    approximate concentrations of the total and soluble rubber    solutions. The area of the band at 990 cm-1 (y axis) is plotted    against the concentration of rubber in units of mg/mL (x-axis) to    construct the calibration curve. The best linear fit for the curve    is then calculated as A=mC+b where A is the area, m is the slope of    the curve, C is the concentration in mg/mL and b is the y intercept.    When more then one type of rubber is present in the polymer the    standards should be made to reflect the expected rubber composition.-   4) Total rubber (Tr) in the sample is calculated using the equation    of the best linear fit of the standards and the initial weight of    the sample.

$\frac{{Tr} = {C*V}}{W}$C is the concentration of rubber in the liquid cell calculated as

$\frac{C = {{Aspl} - b}}{m}$where Asp1 is the integrated area of the 970 cm-1 band in the sample, bis the y-intercept and m is the slope.V is the volume of bromoform used to dissolve the sample.W is the initial weight of the sample.

-   5) Soluble rubber Ts is calculated using the equation of the best    linear fit of the standards and the initial weight of the sample.

$\frac{{Ts} = {C*V}}{W}$C is the concentration of rubber in the liquid cell calculated as

$\frac{C = {{Aspl} - b}}{m}$where Asp1 is the integrated area of the 970 cm-1 band in the sample, bis the y-intercept and m is the slope.V is the volume of bromoform used to dissolve the sample.W is the initial weight of the sample.

The polymerization can be achieved by a number of processes and ispreferably conducted in one or more substantially linear stratified flowor so-called plug-flow type reactors, as described in U.S. Pat. No.2,727,884, which is incorporated herein by reference. In one embodiment,the composition of the present invention is produced using a linearpolymerization process, utilizing one or more polymerization reactors toproduce a rubber modified polymer having a broad monomodal rubberparticle size distribution. In another embodiment, recirculation can becombined with the linear process. Recirculation is a technique wherein aportion of a partially polymerized feed is added back at an earlierstage of the polymerization process. If bimodal particle sizedistributions are desired, it can be accomplished by any acceptablemethod including those disclosed in U.S. Pat. Nos. 4,221,883; 5,240,993;and 4,146,589, all of which are incorporated herein by reference, aswell as in EP-96,447B and EP-892,820. In one aspect, a first mixture ofa solution of a monovinylidene aromatic monomer, optionally anethylenically unsaturated nitrile monomer, and a rubber is masspolymerized in the presence of an initiator under conditions sufficientto form a partially polymerized continuous phase containing polymer anddiscrete particles of highly grafted rubber having a specific volumeaverage diameter. A second rubber-containing mixture is subsequentlyadmixed with the partially polymerized feed under conditions such thatthe previously formed rubber particles remain dispersed throughout thecontinuous polymer phase. The newly added rubber is dispersed asdiscrete particles having a second volume average diameter. Bimodalcompositions can also be obtained by producing each particle size in aseparate reactor, combining both reaction streams and continuing thepolymerization. Alternatively, melt blending can be used to combine twodifferent rubber modified polymers to produce a rubber modified polymerhaving a bimodal particle size distribution, or a composition having twodifferent rubber particle densities.

In a preferred embodiment, the present invention is anacrylonitrile-butadiene-styrene (ABS) rubber modified polymer consistingessentially of:

-   -   a continuous matrix phase comprising a polymer of a        monovinylidene aromatic monomer, and optionally, an        ethylenically unsaturated nitrile monomer, and discrete rubber        particles dispersed in said matrix, said rubber particles        produced from a rubber component comprising from 5 to 100 weight        percent of a functionalized conjugated diene/monovinylidene        aromatic copolymer rubber containing 40 weight percent or less        monovinylidene aromatic monomer and having at least one        functional group per rubber molecule capable of enabling        controlled radical polymerization;        wherein the composition is further characterized by:    -   a) a volume average rubber particle size of from about 0.15 to        0.35 micron,    -   b) a total rubber phase volume between 12 and 45 percent, based        on the total volume of the combination of the matrix phase and        the rubber particles;    -   c) a partial rubber phase volume between 2 and 20 percent        characterized by rubber particles having a volume average        particle size of greater than 0.40 microns; and    -   d) a crosslinked rubber fraction of at least 85 percent by        weight, based on the total weight of the rubber particles.

The rubber modified polymers of the present invention can be used in avariety of applications including injection molding and thermoforming ofrefrigerator liners, household appliances, toys, automotive applicationsand furniture. The rubber modified polymers produced can also haveapplications in the production of articles containing otherthermoplastic polymers, in that the rubber modified polymers haveimproved welding properties when compared to other rubber modifiedpolymers of the prior art. Additionally, the polymers produced can beblended with other polymers for additional applications.

The following examples are provided to illustrate the present invention.The examples are not intended to limit the scope of the presentinvention and they should not be so interpreted. Amounts are in parts byweight unless otherwise indicated.

EXAMPLES The Compositions in TABLE I are prepared using the specifiedprocesses:

Process A—Linear Plug Flow (Used in Comparative Example 2)

A continuous polymerization apparatus composed of three plug flowreactors connected in series, wherein each plug flow reactor is dividedin three zones of equal size, each zone having a separate temperaturecontrol and equipped with an agitator, is continuously charged in zone 1with a feed composed of a rubber component, styrene, acrylonitrile,ethyl benzene and polydimethylsiloxane, at such a rate that the totalresidence time in the apparatus is approximately 7 hours. 1,1-di(t-butylperoxy) cyclohexane is added to the feed line to the first reactor,n-dodecylmercaptan (nDM) (chain transfer agent) is added to differentzones to optimize the rubber particle sizing and the matrix molecularweight. Table 1 contains further details with respect to appliedconditions. After passing through the 3 reactors, the polymerizationmixture is guided to a separation and monomer recovery step using apreheater followed by a devolatilizer and an extruder. The molten resinis stranded and cut in granular pellets. The monomers and ethyl benzeneare recycled and fed to the polymerization apparatus.

Temperature ranges are: (Zone 1, 104–107° C.) (Zone 2 106–110° C.) (Zone3 108–114° C.) (Zone 4 110–116° C.) (Zone 5 110–12° C.) (Zone 6 110–125°C.) (Zone 7 125–140° C.) (Zone 8 140–155° C.) (Zone 9150–165° C.).

Process B—Two Additions of Rubber According to EP-096447 (Used inExamples 3, 4, 5):

Process A with an additional continuous charge of the polymerizationapparatus in zone 6 with a composition equal to the feed charged to zone1 and at a rate of 25 percent relative to the rate of charging zone 1,thus decreasing the residence time from that zone on.

Process C—1 Addition of Rubber to Partial SAN Polymer in AN and StyreneMonomers (Used in 2^(nd) ABS of Example 1)

Process B in which the charge to zone 1 does not contain a rubbercomponent.

Process D—Recirculation (Used in Example 5 and Comparative Example 1)

Process A with a recirculation of 30 percent of the partial polymerstream leaving the second reactor to zone 2 of the first reactor.

Rubber particle size and rubber phase volume measurements are determinedusing Transmission Electron Microscopy Image Analysis, wherein melt flowrate strands are produced by means of an extrusion plastometer at 220°C. and 3.8 kg load. A sample is cut to fit a microtome chuck. The areafor microtomy is trimed to approximately 1 mm2 and stained with OsO4.Ultrathin sections are prepared using standard microtomy techniques. 70nanometer thin sections are collected on Cu grids and are studied in aHitachi H-600 Transmission Electron microscope at 100 kV. Images arecollected digitally as 1024×1024 pixel computer files at threemagnifications with resulting pixel resolutions of 0.005 μm/pixel (highmagnification: 20k×), 0.018 μm/pixel (medium magnification: 6k×), and0.033 μm/pixel (low magnification: 3k×).

The resulting micrographs are analyzed for rubber particle sizedistribution and rubber phase volume by means of the Leica QWin PROsoftware running on an Intel Pentium-based computer with the MicrosoftWindows 98 software. Images from all three magnifications are inspectedmanually to determine which magnifications are useful based on the sizesof particles present. In cases where all particles present are less than0.5 μm, the high-magnification images, only, are used. In cases whereparticles in the range of 0.5 μm to 5 μm are also present, the high andmedium magnification images are used. Further, in cases where particlesgreater than 5 μm are also present, the low magnification images arealso used. Objects in the image less than 5 pixels in area areconsidered to be noise and are ignored during analysis. Manual editingis used to eliminate other artifacts such as knife chatter. Allremaining objects are treated as gel particles and measured. Particlearea is measured and converted to the equivalent circle diameter whichis then reported as the particle size.

Particle sizes are classified into set ranges for graphicalrepresentation and analysis. Raw particle counts at a givenmagnification are converted to particle counts-per-unit area in order tocombine data from multiple magnifications. The counts within aclassification are converted to the fractional volume of material thatwould be present based on the size of the class. These volumes are thenplotted as a function of the class size to create the volumetricsize-distribution. The volumetric size-distribution histograms from thedifferent magnifications are compared for overlap and an optimumtransition point from one magnification to the next is chosen. Thetransition point is usually chosen where the raw counts within a classfrom the higher-magnification drop below about 5 percent of the totalraw counts for that magnification. The combined class data from theappropriate magnifications based on the transition points betweenmagnifications are then used for further calculations of particle sizeand phase volume.

Rubber phase volume Φ in rubber reinforced styrenics resins waspreviously estimated by measuring gel content. Improved resinscontaining such small rubber particles render this method no longerfeasible. Φ can be derived directly from TEM micrographs, assuming thatthe observed rubber phase area fraction S equals Φ. This approachoverestimates Φ, due to section thickness effects. Such effects gainimportance with increasing section thickness and/or decreasing particlesize of the rubber. A stereological correction of S allows calculationof Φ within reasonable error margins:Φ=κ·S where

$\kappa = \frac{2D_{p}}{{3t} + {2D_{p}}}$The projected average diameter Dp is calculated from the resultsobtained from a particle size distribution measurement after correctionfor section thickness.

$D_{p} = \frac{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{3}}}{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{2}}}$whereNi: number of particles in class i after correctiondi: maximum diameter of class im: total number of classesErrors in Φ are found to be mainly due to an inhomogeneous distributionof the rubber.

However, the micrographs also show particles which are not cut throughthe middle. A correction method developed by Scheil [E. Scheil, Z.Anorg. Allgcm. Chem. 201, 259 (1931); E. Scheil, Z. Mellkunde 27(9),199(1935); E. Scheil, Z. Mellkunde 28(11), 240(1936)] and Schwartz [H.A. Schwartz, Metals and Alloys 5(6), 139(1934)] is slightly modified totake the section thickness into account. The measured area of eachrubber particle (ai) is used to calculate the equivalent circle diameterei: this is the diameter of a circle having the same observed area asthe rubber particle. The distribution of ei is classified into mdiscrete size classes across the observed range of particle sizes wherethe size of the class is given as di and the number of particles in eachclass is ni. For example, with m=20 and the size range of 0 to 1 μm, theclass sizes would be 0.05, 0.10, 0.15 . . . 1.0 μm. The classificationsfrom different magnifications are combined as described above. Now thecorrected class counts are given by

$N_{i} = \frac{n_{i} + {\sum\limits_{j = {i + 1}}^{m}{N_{j}\sqrt{d_{j}^{2} - d_{i}^{2}}}} - \sqrt{d_{j}^{2} - d_{i - 1}^{2}}}{t + \sqrt{d_{i}^{2} - d_{i - 1}^{2}}}$whereni: number of particles in class i before correctionand Nm=nm for the largest class, m.Once Ni versus di is obtained, the following parameters are calculated:Number average diameter

$D_{n} = \frac{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}}}{N}$Area average diameter

$D_{a} = \sqrt{\frac{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{2}}}{N}}$Volume average diameter

$D_{v} = \sqrt[3]{\frac{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{3}}}{N}}$Z+1 average diameter D_(z+1=)

$\frac{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{4}}}{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{3}}}$Projection average diameter

$D_{p} = \frac{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{3}}}{\sum\limits_{i = 1}^{m}{N_{i} \cdot d_{i}^{2}}}$Dispersity factor 1

$D_{1} = \frac{D_{v}}{D_{n}}$Dispersity factor 2

$D_{2} = \frac{D_{z + 1}}{D_{n}}$

Intrinsic gloss is measured according to ASTM D2457-97. Intrinsic glossspecimens were molded on an Arburg 170 CMD Allrounder injection moldingmachine, having the following molding conditions: Barrel temperaturesettings of 210, 215, and 220° C.; Nozzle temperature of 225° C., Moldtemperature of 30° C.; Injection pressure: 1500 bar; Holding pressure 50bar; Holding time 6 seconds; Cavity switch pressure: 200 bar; Coolingtime: 30 seconds; and injection speed: 10 cubic centimeters per second(cm³/s).

The dimensions of the molded plaque are 64.2 mm×30.3 mm×2.6 mm.Intrinsic gloss is measured in the center of the plaque on the surfaceat which the pressure is measured. The materials are injected throughone injected point located in the middle of the short side of the mold.During injection molding, the injection pressure switches to holdingpressure when the cavity pressure reaches the pre-set value. Thepressure transducer is located at a distance of 19.2 mm from theinjection point. By using a constant pre-set cavity pressure value, theweight of the molded plaques is the same for materials with differentflow characteristics.

Polishing of the mold is according to SPI-SPE1 Society of PlasticEngineers. Izod impact strength is determined according to ASTM D256-97.Melt Flow Rate is determined according to ASTM D1238-94A. Total energyto break is determined by Instrumented dart impact at 73 F by methodASTM D3763-97a.

Rubber Component 1: Functionalized Rubber

Rubber Component 2: Solprene™ 1322+Functionalized Rubber (50:50)

Rubber Component 3: Solprene™ 1110+Functionalized Rubber (50:50)

Rubber Component 4: Solprene™ 1110+Funct. Rubber+Buna CB HX565(40:40:20)

Rubber Component 5: Solprene™ 1322+Asaprene™ 720 (50:50)

Functionalized Rubber is anionically polymerized 13/87 styrene/butadieneblock copolymer rubber having 13.5 wt. percent styrene terminated with8,8,10,10-Tetramethyl-9-{1-(4-oxyranylmethoxy-phenyl)-ethoxy}-1,5-dioxy-9-aza-spiro{5.51}undecanedescribed in WO 02/48109, having a 5 percent solution viscosity instyrene of 25 cPoise.

Solprene™ 1322, from DYANSOL LLC, is an anionically polymerized 30/70styrene/butadiene diblock copolymer, having a 5 percent sol. visc. instyrene of 25 cPoise.

Solprene™ 1110, from DYNASOL LLC, is an anionically polymerized 15/85styrene-butadiene diblock copolymer having a 5 percent solutionviscosity in styrene of 35 cPoise.

Buna CB HX565, available from Bayer, is an anionically polymerizedbutadiene rubber, coupled with tetrafunctional component tostar-branched structure, and having a 5 percent solution viscosity instyrene of 44 cPoise.

Asaprene™ 720, available from Asahi is an anionically polymerizedbutadiene rubber, coupled with tetrafunctional component tostar-branched structure, and having a 5 percent solution viscosity of 25cPoise.

Acrawax C: N,N′-ethylenebisstearamide wax, available from Lonza PDMSDC50: polydimethylsiloxane with 100 cStokes viscosity, from Dow Corning.

Results are listed in TABLE I.

TABLE I Example 1* 90% 10% 2 3 4 5 Comp1 Comp2 Process A C B B B D D ARubber Component 1 5 2 3 4 3 2 2 Zone 1 Feed Composition Rubbercomponent type 1 None 2 3 4 3 2 2 Rubber component (wt. %) 14 0 14.513.5 13.2 13.5 14.5 14.5 Acrylonitrile (wt. %) 16 20 15.7 17.0 17.0 17.015.7 15.7 Ethyl Benzene (wt. %) 15 15 15.0 15.0 15.0 15.0 15.0 15.0Styrene (wt. %) 55 65 54.65 54.35 54.55 54.35 54.65 54.65 PDMS DC50 (wt.%) 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 1,1-di(t-butyl peroxy)cyclohexane (ppm) 100 200 140 145 145 120 100 140 NDM (to zone 1) (ppm)200 0 350 350 350 0 0 300 NDM (to zone 4) (ppm) 1200 460 0 0 0 1300 12000 NDM (to zone 5) (ppm) 0 0 1700 2000 1700 0 0 1700 NDM (to zone 6)(ppm) 1600 0 0 0 0 0 0 0 NDM (to zone 7) (ppm) 0 1520 0 500 500 750 9000 % Recycling to zone 5 0 6 0 0 0 0 6 % Feed to zone 5 (relative tozone 1) 0 123 25 25 25 0 0 0 Zone 5 Feed composition Rubber componenttype 5 2 3 4 Rubber component (wt. %) 17.5 14.5 13.5 13.2 Acrylonitrile(wt. %) 16 15.7 17.0 17.0 Styrene (wt. %) 51.5 15.0 15.0 15.0 EthylBenzene (wt. %) 15 54.65 54.35 54.55 PDMS DC50 (wt. %) 0.15 0.15 0.150.15 Acrawax C (wt. %) to zone 6 0 0 0 0.9% 0.9% 1.1% 0 0 Recirculationto zone 2 0 0 0 0 0 30 30 0 RPM first reactor 80 120 120 120 120 120 120120 RPM second reactor 60 60 80 80 90 75 80 100 RPM third reactor 30 3020 25 25 25 25 25 End product properties Rubber Particle Size (RPS) Dn(micron) 0.21 0.21 0.24 0.24 0.20 0.16 RPS Dv (micron) 0.24 0.25 0.250.30 0.27 0.24 0.18 RPS D(z + 1) 0.34 0.35 0.42 0.32 0.29 0.21 D₂ =(D(z + 1)/Dn) 1.61 1.67 1.75 1.33 1.45 1.31 Composition Acrawax C (wt.%) 1 0 1.5 1 1.5 1.5 0 Acrylonitrile (%) 22 20.6 21.2 20.4 21.1 19.520.5 Polybutadiene fraction (%) 13.8 15.3 15.5 14.8 15.1 14.6 13.5 TotalRubber (wt. %) 16.2 19.6 17.6 16.3 17.1 18.7 17.3 Total Rubber PhaseVolume Φ (%) 21.0 27.3 31.4 32.3 27.2 30.6 24.5 Rubber Phase Volume >0.4 micron Φ⁺ (%) 2.5 7.9 10.7 14.2 3.8 1.2 0.2 100 × Φ⁺/Φ (%) 12 29 3444 14 4 <1 Mw (/1000) (g/mole) 113 138 125 123 133 131 151 Mn(/1000)(g/mole) 39 47 40 42 48 46 47 Mw/Mn 2.90 2.94 3013 3.15 2.77 2.853.21 % Crosslinked Rubber — 93 94 95 95 99 — Intrinsic Gloss 79 83 82 8183 85 79 MFR(g/10 min) 4.5 3.3 4.8 4.5 4.8 4.8 1.9 Izod(J/m) 246 406 342368 358 224 43 Total Energy (J) 44 43 44 37 36 13 4 *Example 1 is 90 wt.% of product produced with process A and 10 wt. % of a product producedwith process B. % Crosslinked rubber is determined according to theprocess described in the specification.

1. A mass polymerized rubber-modified polymeric composition comprising:a continuous matrix phase comprising a polymer of a monovinylidenearomatic monomer, and optionally, an ethylenically unsaturated nitrilemonomer, and discrete rubber particles dispersed in said matrix, saidrubber particles produced from a rubber component comprising from 5 to100 weight percent of a functionalized diene rubber having at least onefunctional group per rubber molecule capable of enabling controlledradical polymerization; wherein the composition is further characterizedby: a) a volume average rubber particle size of from about 0.15 to 0.35micron, b) a total rubber phase volume between 12 and 45 percent, basedon the total volume of the combination of the matrix phase and therubber particles; c) a partial rubber phase volume between 2 and 20percent characterized by rubber particles having a volume averageparticle size of greater than 0.40 microns; and d) a crosslinked rubberfraction of at least 85 percent by weight, based on the total weight ofthe rubber particles.
 2. The composition of claim 1 wherein the matrixphase comprises a copolymer of styrene and acrylonitrile.
 3. Thecomposition of claim 1 wherein the matrix phase comprises a styrenehomopolymer.
 4. The composition of claim 1 wherein the matrix phasepolymer further comprises butylacrylate, N-phenyl maleimide orcombinations thereof.
 5. The composition of claim 1 wherein the rubbercomponent comprises a functionalized styrene/butadiene block copolymer.6. The composition of claim 5 wherein the styrene/butadiene rubbercomprises at least 5 wt. percent styrene polymer block, based on thetotal weight of the block copolymer.
 7. The composition of claim 6wherein the styrene/butadiene rubber comprises at least 10 wt. percentstyrene polymer block, based on the total weight of the block copolymer.8. The composition of claim 5 wherein the block copolymer isfunctionalized with: 2,2,6,6,-tetramethyl-1-piperidinyloxy (TEMPO);2,2,6,6-tetramethyl-1-[1-[4-(oxiranylmethoxy)phenyl]ethoxy]-piperidine;or3,3,8,8,10,10-hexamethyl-9-[1-[4-(oxiranylmethoxy)phenyl]ethoxy]-1,5-dioxa-9-azaspiro[5.5]undecane.9. The composition of claim 1 wherein the functionalized rubber containsa functional group capable of atom transfer radical polymerization. 10.The composition of claim 1 wherein the functional group is capable ofreversible addition-fragmentation chain transfer polymerization.
 11. Thecomposition of claim 1 wherein the discrete rubber particles have amonomodal particle size distribution of 1.25 or more.
 12. Thecomposition of claim 1 wherein the discrete rubber particles have abimodal particle size distribution, comprising larger rubber particlesand smaller rubber particles.
 13. The composition of claim 12 whereinthe smaller rubber particles are produced from a functionalized rubberand the larger rubber particles are produced from a non-functionalizedrubber.
 14. An article produced from the composition of claim 1.